The present invention relates to a ruthenium alloy sputtering target capable of reducing its oxygen content, reducing the generation of arcing and particles during sputtering, increasing the target strength by improving the sintered density, and improving the deposition quality by strictly restricting the amount of B and P impurities in the target in order to prevent the compositional variability of B and P added in minute amounts to the Si semiconductor.
Since a ruthenium (Ru) alloy has superior thermal stability in addition to having low resistivity and favorable barrier characteristics, it is attracting attention as a deposition material of a semiconductor device; in particular as a gate electrode material and various diffusion barrier materials.
When sintering a pure ruthenium target, dissociation of oxygen occurs near 1100° C., and, even when the oxygen content of the raw material powder is high at 2000 wtppm, it is possible to reduce the oxygen content to less than 100 wtppm with a sintered compact.
For example, Japanese Patent Laid-Open Publication No. H11-50163 (Patent Document 2) describes a high purity ruthenium target manufactured using raw material powder having an oxygen content of 500 ppm wherein the content of alkali metals is less than 1 ppm, content of alkali earth metals is less than 1 ppm, content of radioactive elements is less than 10 ppb, total content of carbon and gas components is less than 500 ppm, oxygen concentration is 100 ppm or less, and purity is 99.995% or higher.
Nevertheless, in the case of a ruthenium alloy, when elements other than ruthenium composing the alloy (hereinafter referred to as “alloy elements”) create oxides easier than ruthenium and form oxides that are more stable than ruthenium, the oxygen that becomes dissociated from ruthenium will react with the alloy elements, and, as a result, the oxygen content of the ruthenium alloy cannot be reduced even after sintering. For example, this tendency is particularly strong with a ruthenium-tantalum alloy, and it is difficult to manufacture a target with a low oxygen content based on the powder sintering method.
For instance, although Patent Document 2 is an invention by the same applicant, even when using the raw material powder (ruthenium powder) described in such Patent Document 2, in the case of forming a ruthenium alloy, the oxygen content became 1000 to 2000 ppm when alloy elements forming stable oxides. Further, even when raw material powder (ruthenium powder) with a lower oxygen content was used, the resulting oxygen content was roughly the same level. This is considered to be because, even when the oxygen content of the raw material powder itself is low, adsorped oxygen exists in large quantities, and the raw material powder is easily oxidized through the mixing process.
As an example of a publicly known ruthenium alloy target, as described in Japanese Patent Laid-Open Publication No. 2004-319410 (Patent Document 1), a commercially available Ru powder that is less than 100 mesh is mixed with Ta powder, subject to hot press molding at a temperature of 1150° C. and a pressure of 15 MPa, and ground with a diamond grindstone at 200 rpm to create a target having a diameter of 125 mmφ and a thickness of 5 mm. Here, since there is no process to eliminate oxygen, the oxygen content is most likely high and the density is most likely low, and this cannot be used in the manufacture process of a semiconductor.
Further, Japanese Patent Laid-Open Publication No. 2002-167668 (Patent Document 3) describes sintering powder obtained by mixing commercially available ruthenium powder and an additive element through mechanical alloying using a ball mill or an attriter or sintering powder alloyed based on the plasma melting method through hot pressing, hot isostatic pressing or plasma sintering method. Here, it is described that to perform degassing in a vacuum or a hydrogen atmosphere at 600 to 900° C. during the hot pressing process is effective.
Nevertheless, since it is only described that degassing is effective to eliminate the adsorped oxygen or the like, oxygen of oxides previously formed from the alloy elements is not eliminated, and it is believed that it would be difficult to manufacture a target having an oxygen content of 1000 ppm or less even when alloy powder is prepared using the plasma melting method at the previous step.
This is because, with the plasma melting method, it is necessary to introduce a plasma formation gas (argon+hydrogen, etc.) having a certain level of pressure into the reaction chamber in order to stably form superhot plasma, and it is considered that oxygen cannot be sufficiently eliminated since it is not possible to achieve a high vacuum. By subjecting the alloy powder obtained with the foregoing method to hot pressing and then HIP, although it is indeed possible to increase the density and suppress the concentration of B and P, the oxygen content will remain high.
As a ruthenium alloy, when alloy elements such as tantalum and niobium which form oxides easier than ruthenium are mixed on a macroscale, deoxidization will become difficult, and this is notable when the composition of alloy elements is 5 at % or greater, and particularly when the composition is 10 at % to 60 at %.
Meanwhile, when a ruthenium alloy is to be used as a deposition material of a semiconductor device, in particular as a gate electrode material and various diffusion barrier materials, composition in the foregoing range will be required. In conventional technology, the oxygen content being high in excess of 1000 ppm was inevitable. Thus, when sputtering is performed using such a target, there is a problem in that the quality of the deposition will decrease because the target strength will be weak as a result of the sintered density being low, and the generation of arcing and particles will become notable during sputtering, and it was not possible to obtain a target material having the characteristics required for a semiconductor device.